Agricultural products, such as vegetables and flowers are grown on a large scale in greenhouses throughout the world. During daylight hours, growing agricultural products introduce water vapor into a greenhouse and extract carbon dioxide from the air. Often, the addition of heat to a greenhouse on a daily basis is required depending on geographic location and season of the year. In some locations, heat is needed only at night while in other locations, heat is needed during all or part of the day. In all cases where a greenhouse is heated, some of the heat goes to evaporating water found in great abundance in a greenhouse. The vapor thus produced adds to the vapor produced by evapotranspiration of the growing products in the greenhouse with the result that the humidity in the greenhouse often approaches saturation. This is an unhealthy condition for most plants: and for many years, the solution was to open the greenhouse to ambient conditions exchanging the air in the greenhouse with ambient air that is generally cooler and dryer. Such a solution is energetically inefficient; and for this reason, attention has recently turned to utilizing direct contact air-brine vapor heat exchangers in the greenhouse for the purpose of drying the air. Brine is hygroscopic because the vapor pressure at the air/brine interface at a given temperature will be less than the vapor pressure of vapor in the air at the same temperature.
One technique that might be applicable to greenhouses is disclosed in U.S. Pat. No. 4,355,683, in which air in an enclosure is passed through a drying tower where the air is contacted with a brine shower causing water vapor in the air to condense on the brine droplets thereby drying the air and producing diluted brine that must be reconcentrated before being cycled back into the tower. In this patent, the latent heat of condensation added to the diluted brine during the conditioning process is rejected to the atmosphere in a heat exchanger and is thus wasted.
More efficient use of this latent heat of condensation is found in co-pending U.S. Pat. applications Ser. No. 483,741 filed Apr. 11, 1983 and U.S. Pat. Ser. No. 479,009 filed Mar. 23, 1983 which disclose temporarily storing the latent heat in the brine, and contacting the air in the enclosure with the brine during the night when the air in the enclosure will be cooler than the brine. Stored heat in the brine is thus transferred to the air in the enclosure by a reduction in the sensible heat of the brine.
In all of these techniques, reconcentration of the brine is a necessity for continuous operation. In the '683 patent, this is accomplished by heating the diluted brine and contacting it with ambient air in another tower. In this situation, the vapor pressure at the air-brine interface of the heated brine will exceed the vapor pressure of ambient air with the result that water in the brine evaporates producing concentrated brine that is returned to the tower associated with the enclosure. The heat input in the regeneration process is the latent heat of evaporation of the water removed from the brine; and, needless to say, none of this heat is recovered. This is the situation in all techniques presently known for concentrating brine used to condition the air in an enclosure: and it is an object of the present invention to provide a new and improved method of a means for conditioning air in an enclosure using an air-brine-vapor heat exchanger wherein heat used to reconcentrate the brine is transferred to the enclosure rather than wasted.